Pipe joint made of resin

ABSTRACT

The invention provides a pipe joint made of resin in which a predetermined pressing force in the axial direction corresponding to a fastening torque of a union nut can be obtained, and the strength of threads can be enhanced. Each of the threads of an external thread portion of a joint body and an internal thread portion of a union nut is formed asd an asymmetrical trapezoid, an inclined angle α 1  of first flanks of the asymmetrical trapezoidal threads which contact with each other by fastening the union nut is set to 70 to 90°, and an included angle α 2  of the flanks opposite to the first flanks is set to 40 to 80°, and wherein the joint body defines a sealing portion the angle and direction of taper of which is defined by an angle θ 0 , said external thread is defined by an angle θ 1 , where θ 1 =α 1  and wherein θ 0 &lt;θ 1  and |cos θ 0 |&gt;|cos θ 1 |.

CROSS REFERENCE TO RELATED APPLICATION

This application is a CIP of application Ser. No. 09/901,639 Filed onJul. 11, 2001 now U.S. Pat. No. 6,517,123.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pipe joint made of resin which ispreferably used in piping for a liquid having high purity or ultrapurewater to be handled in a production process in, for example, theproduction of semiconductor devices, the production of medical equipmentand medicines, for food processing, and in the chemical industry.

2. Description of the Prior Art

Conventionally, as pipe joints made of resin of this kind, those havinga configuration like that shown in FIGS. 4 to 6 are known. Among them,the pipe joint made of resin shown in FIG. 4 (see Japanese Utility ModelPublication No. 7-20471) comprises a joint body 1, a sleeve 2, and aunion nut 3 which are made of resin. In the joint body 1, a pipereceiving port 5 is formed at one end in the axial direction. A firstsealing portion 6 is formed in an inner area of the pipe receiving port5, and a second sealing portion 7 is formed in an entrance area of thepipe receiving port 5 so that the sealing portions intersect the axis Cof the joint body 1. An external thread portion 9 is formed on the outerperiphery of the pipe receiving port 5. In the sleeve 2, a fittingportion 10 having an outer diameter that allows the portion to be fittedinto the receiving port 5 of the joint body 1 is formed in an inner endportion in the axial direction, and a bulge portion 15 having amountain-like section shape is formed in an outer end side in the axialdirection. The sleeve 2 is pressingly inserted into one end portion 17of a tube 11 made of resin under a state where the fining portion 10projects outwardly. As a result of this press insertion, the diameter ofthe one end portion 17 of the tube 11 is increased. An inner end sealingportion 13 which abuts against the sealing portion 6 of the joint body 1is formed in an end portion of the fitting portion 10, and an outerperipheral sealing face 18 which abuts against the sealing portion 7 ofthe pipe receiving port 5 is formed in a place corresponding to thebulge portion 15. In the union nut 3, an internal thread portion 20which is to be screwed to the external thread portion 9 of the jointbody 1 is formed.

The one end portion 17 of the tube 11 into which the sleeve 2 ispressingly inserted is inserted into the receiving port 5 of the jointbody 1. Under this state, the internal thread portion 20 of the unionnut 3 which is previously loosely fitted onto the outer periphery of theone end portion 17 of the tube 11 is screw-fastened to the externalthread portion 9 of the joint body 1. This fastening causes the sleeve 2to be pressed in the axial direction, so that the inner end sealingportion 13 and the outer peripheral sealing face 18 of the sleeve 2 abutagainst the sealing portions 6 and 7 of the pipe receiving port 5 of thejoint body 1, respectively, thereby exerting a sealing function.

In the pipe joint made of resin shown in FIG. 5, a tapered sealingportion 30 in which the diameter is gradually reduced toward the innerside in the axial direction is formed in an entrance area of a receivingport 5 of a joint body 1 into which the one end portion 17 of the tube11 made of resin is to be inserted, and a sealing portion 31 which abutsagainst a tapered sealing portion 30 is formed in the inner end of asleeve 2. The sleeve 2 is fitted onto the one end portion 17 of the tube11, whereby a bulge portion 32 which is locally projected toward theradially inner side is formed on the one end portion 17 of the tube 11.The internal thread portion 20 of the union nut 3 which is previouslyloosely fitted onto the outer periphery of the one end portion 17 of thetube 11 is fastened to an external thread portion 9 of the joint body 1.This fastening causes the sleeve 2 to be pressed in the axial direction,so that sealing portions 30 and 31 abut against each other, therebyexerting a sealing function.

In the pipe joint made of resin shown in FIG. 6, a tapered sealingportion 33 in which the diameter is gradually reduced toward the innerside in the axial direction is formed in an entrance area of a receivingport 5 of a joint body 1 into which the one end portion 17 of the tube11 made of resin is to be inserted. A sleeve 2 which has an outerperipheral wall 34 having a trapezoidal section shape is pressinglyinserted into the inner periphery of the one end portion 17 of the tube11. As a result of this press insertion, a bulge portion 35 which islocally projected toward the radially outer side along the outerperipheral wall 34 of the sleeve 2 is formed on the tube 11. Theinternal thread portion 20 of the union nut 3 which is previouslyloosely fitted onto the outer periphery of the one end portion 17 of thetube 11 is fastened to an external thread portion 9 of the joint body 1,whereby the bulge portion 35 of the tube 11 and the sleeve 2 are pressedagainst the joint body 1 and an inclined face 36 on the tube end side ofthe bulge portion 35 is pressed against the tapered sealing portion 33in the axial direction, so as to exert a sealing force.

As described above, all of the conventional pipe joints made of resinshown in FIGS. 4 to 6 comprise: the joint body 1 which is made of resin,and which has the pipe receiving port 5 in one end portion, and theexternal thread portion 9 on the outer periphery of the pipe receivingport 5; the sleeve 2 which is made of resin, and which is to bepressingly inserted into the inner or outer periphery of the one endportion 17 of the tube 11 made of resin to be integrated therewith; andthe union nut 3 which is made of resin, which is loosely fitted onto theouter periphery of the one end portion 17 of the tube 11, and which isscrewed via the internal thread portion 20 to the external threadportion 9 of the joint body 1. The one end portion 17 of the tube 11into which the sleeve 2 is pressingly inserted to be integratedtherewith is inserted into the pipe receiving port 5 of the joint body1. The gap between the one end portion 17 of the tube 11 and the pipereceiving port 5 of the joint body 1 is sealed in a water blockingmanner via the sleeve 2 which is pressed against the joint body 1 byfastening the union nut 3.

In all of the conventional pipe joints made of resin, the externalthread portion 9 of the joint body 1 and the internal thread portion 20of the union nut 3 use triangular threads according to usual threadstandards. Such triangular threads have an included angle of 55° or 60°(see FIG. 4).

However, usual thread standards are originally introduced for metals,and, in some cases, are not suitable to threads for resin such as thosefor a pipe joint made of resin because, when a pipe joint is made ofresin, creep deformation which advances over time under a constant loadis largely affected by the load and the temperature.

In the pipe joint made of resin in which the sleeve 2 and the joint body1 are pressed against each other by fastening the union nut 3, a creepphenomenon and stress relaxation due to the phenomenon occur in aportion where the sleeve 2 and the joint body 1 are pressed, therebycausing the liquid to leak or the tube 11 to slip off. Therefore,functions which are exerted by pressing the two components, i.e., thesleeve 2 and the joint body 1, such as the sealing function, and thefunction of preventing the tube 11 from slipping off must be ensured.Therefore, it is required to set a pressing force which is necessary andsufficient for exerting functions such as the sealing function. In thecase where a creep phenomenon or the like occurs and the union nut 3 isto be further fastened, adjustment of the pressing force must beperformed at a higher degree.

As the resin material of a pipe joint of this kind, fluororesin whichhas excellent heat resistance and chemical resistance is usually used.When triangular threads according to usual metal thread standards areapplied to the internal thread portion 20 of the union nut 3 and theexternal thread portion 9 of the joint body 1 which are made of suchfluororesin, it is sometimes difficult to obtain a desired pressingforce in the axial direction corresponding to the fastening torque ofthe union nut 3 under severe and extreme use conditions which are muchseverer than usual use conditions, such as those in which thetemperature of a fluid to be transported is higher than 200° C., or thepressure of the fluid is higher than 1 MPa. Even when the internal andexternal thread portions 20 and 9 are not broken, there arises a casewhere the sealing property and the resistance to tube slipping off whichare required in a pipe joint are not sufficiently satisfied.Specifically, a remarkable creep phenomenon of the resin material maycause a case where the force (fastening torque) of rotating the unionnut 3 in the fastening direction exceeds the strength of the threads andthe threads are broken, or that where the internal thread portion 20 ofthe union nut 3 slips over threads of the external thread portion 9 ofthe joint body 1, and the union nut 3 swells toward the radially outerside, so that the internal thread portion 20 is disengaged from theexternal thread portion 9 and the union nut is freely rotated.

SUMMARY OF THE INVENTION

The present invention solves the noted problems. It is an object of theinvention to provide a pipe joint made of resin in which an asymmetricaltrapezoidal thread is used as a section shape of threads of a union nutand a joint body that are made of resin, improvements are then made onthe setting of the included angle, whereby, even under severe useconditions in which a fluid of a high temperature and a high pressure istransported, and

which are much more severe than usual use conditions, a predeterminedpressing force in the axial direction corresponding to the fasteningtorque of the union nut can be obtained, and the strength of the threadscan be enhance.

The pipe joint made of resin of the invention comprises: a joint body 1which is made of resin, and which has a pipe receiving port 5 at one endportion, and an external thread portion 9 on an outer periphery of thepipe receiving port; a sleeve 2 which is made of resin, and which is tobe pressingly inserted into an inner or outer periphery of an one endportion 17 of a tube 11 made of resin, to be integrated therewith; and aunion nut 3 which is made of resin, and which is loosely fitted onto theouter periphery of the one end portion 17 of tube 11, and which isscrewed via an internal thread portion 20 to the external thread portion9 of the joint body.

The pipe joint made of resin of the invention comprises: a joint body 1which is made of resin, and which has a pipe receiving port 5 in one endportion, and an external thread portion 9 on an outer periphery of thepipe receiving port; a sleeve 2 which is made of resin, and which is tobe pressingly inserted into an inner or outer periphery of an one endportion 17 of a tube 11 made of resin, to be integrated therewith; and aunion nut 3 which is made of resin, and which is loosely fitted onto theouter periphery of the one end portion 17 of the tube 11, and which isscrewed via an internal thread portion 20 to the external thread portion9 of the joint body 1. The one end portion 17 of the tube 11 into whichthe sleeve 2 is pressingly inserted to be integrated therewith isinserted into the pipe receiving port 5 of the joint body 1. A gapbetween the one end portion 17 of the tube 11 and the pipe receivingport 5 of the joint body 1 is sealed via the sleeve 2 which is pressedagainst the joint body 1 by fastening the union nut 3. The pipe jointmade of resin is characterized in that a section shape of each of thethreads of the external thread portion 9 of the joint body 1 and theinternal thread portion 20 of the union nut 3 is formed as anasymmetrical trapezoid, an included angle α₁ of flanks 9 a and 20 a ofthe asymmetrical trapezoidal threads which are in contact with eachother by fastening the union nut 3 is set to 70 to 90°, and an includedangle α₂ of flanks 9 b and 20 b opposite to the flanks is set to 40 to80° (which is an angle smaller than the included angle α₁). See FIG. 2.

According to the thus configured pipe joint made of resin of theinvention, the external thread portion 9 of the joint body 1 and theinternal thread portion 20 of the union nut 3 are formed as asymmetricaltrapezoidal threads, and the included angle of the flanks 9 a and 20 aof the asymmetrical trapezoidal threads which are made in contact witheach other by fastening the union nut 3 is set to 70 to 90°. Therefore,fastening of the union nut 3 can be surely done and this can ensure apressing force in the axial direction which is larger than that obtainedin a conventional case where the above-mentioned triangular threads ofan included angle of 27.5° or 30° are used. Since the included angle ofthe flanks 9 b and 20 b opposite to the flanks is set to 40 to 80°(which is an angle smaller than the included angle α₁), the threads cansufficiently withstand a shearing load which is applied to the threadsas a result of exerting a high fastening torque, and a friction force ofa relatively higher degree can be obtained so as to ensure also alocking effect.

When the included angle of the flanks 9 a and 20 a of the asymmetricaltrapezoidal threads is smaller than 70°, a necessary and sufficientpressing force cannot be obtained in the same manner as a conventionalcase where the above-mentioned triangular threads of an included angleof 27.5° or 30° are used. When the included angle of the other flanks 9b and 20 b of the asymmetrical trapezoidal threads is smaller than 40°,threads of a sufficient height cannot be obtained at a predeterminedpitch, and, when the included angle is larger than 80°, a high fasteningtorque of the union nut 3 may cause the threads to be cracked or broken,and the locking effect is low.

In this way, the external thread portion 9 of the joint body 1 and theinternal thread portion 20 of the union nut 3 have a structure in whicha large pressing force in the axial direction corresponding to thefastening torque can be obtained, and the strength of the threads isenhanced so that the threads can withstand a high fastening torque ofthe union nut 3. Even when a high fastening torque of the union nut 3 isapplied, the threads of the internal thread portion are prevented frommoving toward the radially outer side to cause the union nut to befreely rotated. According to this configuration, in addition to the casewhere the temperature of the liquid to be transported is the ordinarytemperature (room temperature), even in the case where the liquid to betransported is a fluid of a high temperature (hot water of 200° C.), therotation amount (the number of rotations and the rotation angle) of theunion nut 3 for stably exerting the sealing property and the resistanceto tube slipping off is extremely stabilized. Therefore, a pressingforce required for the sealing property and the resistance to tubeslipping off can be exerted by giving only a constant rotation amount tothe union nut 3.

As described above, according to the invention, the external threadportion of the joint body and the internal thread portion of the unionnut have a structure in which, even under severe use conditions whereina fluid of a high temperature and a high pressure is transported, andwhich are much more severe than usual use conditions, a large pressingforce in the axial direction can be produced, and the strength of thethreads is enhanced so that the threads can withstand a high fasteningtorque of the union nut. Even when a high fastening torque of the unionnut is applied, moreover, the threads of the internal thread portion canbe prevented from moving toward the radially outer side to cause theunion nut to be freely rotated. Therefore, the invention attains aneffect that, in both the cases where the liquid to be transported is afluid of the ordinary temperature, and where the liquid is a fluid of ahigh temperature, a pressing force required for the sealing property andthe resistance to tube slipping off, and the joint can be suitable usedas a pipe joint made of resin can be exerted by giving only a constantrotation amount to the union nut.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of a pipe joint made of resin which is anembodiment of the invention;

FIG. 2 is an enlarged section view of main portions of the pipe jointmade of resin shown in FIG. 1;

FIG. 3 is a half section view of a pipe joint made of resin which isanother embodiment of the invention;

FIG. 4 is a half section view of a pipe joint made of resin of theconventional art;

FIG. 5 is a half section view of another pipe joint made of resin of theconventional art; and

FIG. 6 is a half section view of a further pipe joint made of resin ofthe conventional art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the invention in which the invention is applied to thepipe joint made of resin shown in FIG. 1 will be described. Referring toFIGS. 1 and 2, the pipe joint made of resin comprises a joint body 1, asleeve 2, and a union nut 3 which are made of a resin having excellentheat resistance and chemical resistance, such as fluororesin. The pipejoint is identical in the general configuration with the pipe joint madeof resin of the conventional art shown in FIG. 4, but are differenttherefrom in the structures of the external thread portion 9 of thejoint body 1 and the internal thread portion 20 of the union nut 3.

In the joint body 1, a pipe receiving port 5 is formed at least at oneend of a cylindrical body portion 4, a sealing portion 6 is formed in aninner area of the pipe receiving port 5 so that the sealing portionintersects the axis C of the joint body 1, and a sealing portion 7 isformed in an entrance area of the pipe receiving port 5 so that thesealing portion intersect the axis C. An external thread portion 9 isformed on the outer periphery of the pipe receiving port 5. The innerdiameter of the pipe receiving port 5 is larger than that of the bodyportion 4. In the inner area of the pipe receiving port 5, the sealingportion 6 is formed by a tapered face which is smaller in diameter asviewed when one moves further toward an outer side in the axialdirection and then reaches the inner radial face of the body portion 4.On the other hand, the sealing portion 7 is formed by a tapered facewhich is larger in diameter as viewed when one moves further from theinner area of the pipe receiving port 5 toward an outer side in theaxial direction and then reaches the end face of the pipe receiving port5.

In the sleeve 2, a fining portion 10 having an outer diameter thatallows the portion to be fitted into the receiving port 5 of the jointbody 1 is formed in an inner end portion, and a press insertion portion12 is formed continuously with the fitting portion 10. In the pressinsertion portion, the outer diameter of the vicinity of the portioncontinuous with the fitting portion 10 is smaller by a valuecorresponding to the thickness of the tube 11 made of resin such asfluororesin. The inner periphery of the sleeve 2 is formed so as to bein a same direction condition or have an inner diameter which is equalto or substantially equal to the inner diameters of the innerperipheries of the tube 11 and the body portion 4 of the joint body 1,so as not to impede movement (flow) of a fluid. An inner end sealingportion 13 which abuts against the sealing portion 6, and which isconfigured as a tapered face is formed in an end portion of the sleeve2. By contrast, a tapered outer end sealing portion 14 is formed on theouter periphery of the outer end portion of the sleeve 2, i.e., theouter periphery of the press insertion portion 12. In the outer endsealing portion 14, the diameter is larger as viewed when one movesfurther from the outer end toward an inner side in the axial direction,and the outer end intersects the inner periphery of the sleeve 2. Thediameter of the apex of the outer end sealing portion 14 is set to belarger than at least the outer diameter of the press insertion portion12 of the portion continuous with the fitting portion 10. Namely, thelarger-diameter side of the outer end sealing portion 14 is formed as abulge portion 15 which has a mountain-like section shape, and which isformed on the outer peripheral face in the outer end side of the sleeve2. A tapered face 16 in which the diameter becomes smaller from the apexof the bulge portion 15 to the inner end side of the sleeve 2 is formedso that the inclination angle is substantially equal to that of thesealing portion 7 of the joint body 1, and, when the inner end sealingportion 13 abuts against the sealing portion 6, the gap through whichthe sealing portion 7 is opposed to the tapered face 16 corresponds tothe thickness of the tube 11.

The thus configures sleeve 2 is pressingly inserted into the one endportion 17 of the tube 11 to be integrally coupled to the tube 11 undera state where the press insertion portion 12 is pressingly inserted intothe one end portion 17 of the tube 11 to increase the diameter of theperipheral wall of the one end portion 17 of the tube 11 and the fittingportion 10 of the sleeve 2 projects from the one end portion 17 of thetube 11. In a state where the one end portion 17 of the tube 11 isinserted into the pipe receiving port 5, the inner end sealing portion13 abuts against the sealing portion 6 of the joint body 1 to exert asealing function, and the outer end sealing portion 14 abuts against theinner face of the inclined portion of the one end portion 17 of the tube11 to exert a sealing function. The one end portion 17 of the tube 11 isclamped in an inclined state between the sealing portion 7 of the jointbody 1 and the tapered face 16 of the sleeve 2. Namely, the outerperipheral face of the tube 11 which is deformed along the tapered face16 of the sleeve 2 serves as an outer peripheral sealing face 18 to abutagainst the sealing portion 7, thereby exerting a sealing function.

In the union nut 3, an internal thread portion 20 which is to be screwedto the external thread portion 9 of the joint body 1 is formed on theinner peripheral face of the cylindrical portion, and an annular flangeportion 21 which extends from the outer end toward the axial center isformed. A pressing edge portion 22 is formed on the inner end side ofthe inner peripheral face of the flange portion 21. The pressing edgeportion 22 is formed so that the pressing edge portion 22 is positionedcloser to the axial center than the apex of the bulge portion 15 of thesleeve 2 and also the outer diameter of the portion continuous with thefitting portion 10.

In the thus configured pipe joint made of resin, the invention ischaracterized in the structures of the external thread portion 9 of thejoint body 1 and the internal thread portion 20 of the union nut 3.

The section shape of each of the threads of the external thread portion9 of the joint body 1 and the internal thread portion 20 of the unionnut 3 is formed as an asymmetrical trapezoid, an included angle α₁ offirst flanks 91 and 20 a of the assymmetrical trapezoidal threads whichare made in contact with each other by fastening the union nut 3 is setto 70 to 90°, and an included angle α₂ of second flanks 9 b and 20 bopposite to the flanks is set to 40 to 80°. In the above, α₁>α₂.

In the thus configured pipe joint made of resin, the one end portion 17of the tube 11 into which the press insertion portion 12 of the sleeve 2is pressingly inserted is inserted into the receiving port 5 of thejoint body 1, to cause the inner end sealing portion 13 to abut againstthe sealing portions 6. Thereafter, the internal thread portion 20 ofthe union nut 3 which is previously loosely fitted onto the outerperiphery of the one end portion of the tube 11 is screw-fastened to theexternal thread portion 9 of the joint body 1, and rotated in thefastening direction A. As a result of this fastening rotation of theunion nut 3, a large pressing force in the axial direction correspondingto the fastening torque is generated via the contacts of the flanks 20 aand 9 a of the internal and external thread portions 20 and 9 and havingan included angle of 70 to 90°. Therefore, the sleeve 2 is stronglypressed against the joint body 1 by the pressing edge portion 22 of theunion nut 3. This pressing action causes the sleeve 2 to be stronglyclamped in the axial direction by the pressing edge portion 22 of theunion nut 3 and the sealing portion 6 of the joint body 1, and the oneend portion 17 of the tube 11 is connected to the joint body 1 in asealed state.

Between the flanks 20 a and 9 a of the internal and external threadportions 20 and 9 and having an included angle of 70 to 90°, thereoccurs less slip. Even when the union nut 3 is strongly fastened,therefore, the threads of the internal thread portion 20 can beprevented from moving toward the radially outer side to cause the unionnut to be freely rotated.

Since the included angle of the opposite flanks 9 b and 20 b of theinternal and external thread portions 20 and 9 is set to an angle of 40to 80° which is smaller than the included angle of the flanks 20 a and 9a, the threads of the internal and external thread portions 20 and 9were able to sufficiently withstand a high fastening torque of the unionnut 3, and shearing fracture did not occur.

In this connected state of the tube 11, the one end portion 17 of thetube 11 is clamped between the sleeve 2 and the union nut 3 which areclamped in the axial direction as described above, and also by the pressinsertion portion 12 of the sleeve 2 and the sealing portion 7 of thepipe receiving port 5, and locally clamped by the outer end sealingportion 14 of the sleeve 2 and the pressing edge portion 22 of thesleeve 2. Therefore, the tube 11 can be held by a high resistance toslipping off so as to be prevented from moving to slip off. The sealingportion 6 of the joint body 1, and the inner end sealing portion 13 ofthe sleeve 2 are pressingly contacted to each other to produce a strongadhering force therebetween. At the same time, the sealing portion 7 ofthe joint body 1 is pressingly contacted to the outer peripheral sealingface 18 of the tube 11, and the outer end sealing portion 14 of thesleeve 2 is pressingly contacted to the inner face of the inclinedportion of the tube 11, whereby a strong sealing force is producedbetween the contacting components so that the gaps therebetween aresealed by the both faces of the one end portion 17 of the tube 11.

As described above, sealing is performed between the joint body 1 andthe sleeve 2, and between the sleeve 2 and the tube 11. Furthermore,sealing is performed between the joint body 1 and the tube 11. Thesealing function and the function of preventing the tube 11 fromslipping off can be maintained by the strong pressing force exerted bythe union nut 3. When a fluid of a high temperature (hot water of 200°C.) is transported and a further fastening operation must beadditionally performed, a required pressing force can be exerted bygiving only a substantially constant rotation amount to the union nut 3.In addition to the case of a fluid of the ordinary temperature, even inthe case of a fluid of a high temperature, therefore, the excellentsealing property is ensured so that leakage of the fluid or entry of aforeign substance can be surely prevented from occurring, whereby thereliability of the sealing property can be enhanced. Moreover, the tube11 can be surely prevented from slipping off.

The invention can be similarly applied also to a pipe joint made ofresin having the configuration shown in FIG. 3, and the above-mentionedpipe joints made of resin respectively having the configurations shownin FIGS. 5 and 6, in addition to the pipe joint made of resin of theabove-described embodiment.

In the pipe joint made of resin shown in FIG. 3, a cylindrical sealingportion 26 which is projected outward in the axial direction and moreoutward in a radial direction than a protruding inner end face 25 whichabuts against the sealing portion 6 in the inner area of the pipereceiving port 5 of the joint body 1 is formed in a protruding portion23 of the sleeve 2 that protrudes from the one end portion 17 of thetube 11. An annular groove 28 is formed more outward in a radialdirection than the sealing portion 6 in the inner area of the pipereceiving port 5 of the joint body 1. The annular groove 28 is used forgenerating a surface pressure in a radial direction in accordance withpress insertion of the cylindrical sealing portion 26, thereby formingthe sealing portion 7. In this case, sealing is performed at leastbetween the outer periphery of the cylindrical sealing portion 26 andthat in the annular groove 28. The other configuration is substantiallyidentical with that of the pipe joint made of resin shown in FIG. 1.

Also in the pipe joint made of resin, when the external thread portion 9of the joint body 1 and the internal thread portion 20 of the union nut3 are configured in the same manner as those of the above-mentionedembodiment, a structure is obtained in which, while generating a largepressing force in the axial direction, the strength of the threads isenhanced so that the threads can withstand a high fastening torque ofthe union nut 3. Therefore, it is possible to attain the same effect asthat described above, namely, the effect that, in both the cases of afluid of the ordinary temperature and that of a high temperature, apressing force required for the sealing property, the resistance to tubeslipping off, and the like can be exerted by giving only a constantrotation amount to the union nut 3.

As shown in FIGS. 1 and 3, θ₀ marks the angle and direction of the taperof sealing portion 6 against the taper surface 13 of the joint body 1relative to the axis C. θ₁ is the angle of external thread portion flank9 b, 20 b, as illustrated in FIG. 2, also relative to axis C. In allembodiments, the value of angle θ₀ is less than the value of angle θ₁(i.e., θ₀<θ₁). Actually, in case of reciting only the condition ofθ₀<θ₁, it cannot include a joint embodiment of the present invention asshown in FIG. 3 because the direction of the taper surface 13 of thejoint body 1 in FIG. 1 is opposite to that of the joint in FIG. 3.

For the joints of FIGS. 1 and 3, angles θ₀ and θ₁ can be used todetermine the coefficients of conversion of axial component forces.Specifically, the absolute value of the cosine of θ₀, or |cos θ₀|, isthe coefficient of conversion of an axial component of force for a forcewhich presses the sealing portion 6 against the taper surface 13 of thejoint body 1. The absolute value of the cosine of θ₁, or |cos θ₁|,equates to the coefficient of conversion of an axial component force ofa force exerted on the side of a screw thread 9, when a torque isapplied to union nut 3, thereby pressing sleeve 2 against joint body 1.In any embodiment, in addition to the above condition that θ₀<θ₁, thecondition |cos θ₀|>|cos θ₁| exists.

As stated above |cos θ₀| and |cos θ₀| are the coefficients of conversionof the axial component force. Assuming that a force F for advancing theinner ring to the inner area of the joint body, which is created byscrewing advancement of nut 3, exists, the force required for screwingadvancement of nut 3 and the force for pressing the inner ring againstthe joint body 1 are shown as below. $\begin{matrix}\underset{\_}{{Force}\mspace{14mu}{required}\mspace{14mu}{for}\mspace{14mu}{screwing}} \\\underset{\_}{{advancement}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{nut}}\end{matrix} = \frac{F}{\left. {\underset{\_}{\left| {\cos\mspace{14mu}\theta} \right.}}_{1}\downarrow \right.}$$\begin{matrix}\underset{\_}{{Force}\mspace{14mu}{for}\mspace{14mu}{pressing}\mspace{14mu}{the}\mspace{14mu}{inner}} \\\underset{\_}{{ring}\mspace{14mu}{against}\mspace{14mu}{the}\mspace{14mu}{joint}\mspace{14mu}{body}}\end{matrix} = \frac{F}{\left. {\underset{\_}{\left| {\cos\mspace{14mu}\theta} \right.}}_{0}\downarrow \right.}$

The relationship between the force required for screwing the advancementof the force for pressing the inner ring against the joint body can bedescribed as:$\frac{F}{\left. {\underset{\_}{\left| {\cos\mspace{14mu}\theta} \right.}}_{1}\downarrow \right.} \geq \frac{F}{\left. {\underset{\_}{\left| {\cos\mspace{14mu}\theta} \right.}}_{1}\downarrow \right.}$

This means that the pressing force of the inner ring is smaller than theforce of screwing advancement of the nut. Therefore, even though the nutis screwingly advanced by a large torque, the force |cos θ₁|/|cos θ₀| isless than one time as strong as a thrust to be generated by the pressingforce of the inner ring. In other words, the joint has a structure whichfacilitates slight adjustment of the pressing force of the inner ring(in the same way as a screw of a micrometer.)

As the joint is made of synthetic resin, creep phenomenon willinvariably appear. So, in order to delay the appearance of creep, it isrequired to strictly control the pressing force within in the join.Since relations of |cos θ₀>|cos θ₁| exists, it is possible to slightlyadjust the pressing force and ensures maintenance of the jointefficiency. The present invention has a structure that allows arelatively small pressing force compared to the thrust of the nut.

In each of the pipe joints made of resin shown in FIGS. 5 and 6, whenthe external thread portion 9 of the joint body 1 and the internalthread portion 20 of the union nut 3 are configured in the same manneras the above-described embodiment, a structure is obtained in which,while generating a large pressing force in the axial direction, thestrength of the threads is enhanced so that the threads can withstand ahigh fastening torque of the union nut 3. Therefore, it I possible toattain the same effect as that described above, namely, the effect that,in both cases of a fluid of ordinary temperature and that of a hightemperature, a pressing force required for the sealing property, theresistance to tube slipping off, and the like can be exerted by givingonly a constant rotation amount to the union nut 3.

1. A pipe joint made of resin, comprising: a joint body which is made ofresin, said joint body having a pipe receiving port at one end portion,and an external thread portion on an outer periphery of said pipereceiving port; a sleeve which is made of resin, and which is pressinglyinserted into an inner or outer periphery of one end portion of a tubemade of resin, to be integrated therewith; and a union nut which is madeof resin, which has an internal thread portion, and which is looselyfitted onto the outer periphery of said one end portion of said tube,and which is screwed via said internal thread portion to said externalthread portion of said joint body, said one end portion of said tubeinto which said sleeve is pressingly inserted to be integrated therewithbeing inserted into said pipe receiving port, a gap between said one endportion of said tube and said pipe receiving port of said joint bodybeing sealed via said sleeve which is pressed against said joint body byfastening said union nut, wherein: a section shape of each thread ofsaid external thread portion of said joint body and said internal threadportion of said union nut is formed as an asymmetrical trapezoid,defining a first flank and a second flank and having an included angleof said first flanks of said asymmetrical trapezoidal which contact witheach other by fastening said union nut is set to 70 to 90°, and anincluded angle of said second flanks opposite to said first flanks isset to 40 to 80°, wherein said joint body defines a sealing portion theangle and direction of taper of which is defined by an angle θ₀, saidexternal thread is defined by an angle θ_(1,) and wherein θ₀<θ₁ and |cosθ₀|>|cos θ₁|.
 2. A pipe joint made of resin, comprising: a joint bodywhich is made of resin, said joint body having a pipe receiving port inone end portion, and an external thread portion on an outer periphery ofsaid pipe receiving port; a sleeve which is made of resin, which is tobe pressingly inserted into an inner periphery of an one end portion ofa tube made of resin, and in which an inner end sealing portion isformed in an inner end portion; and a union nut which is made of resin,which has an internal thread portion, which is loosely fitted onto anouter periphery of said one end portion of said tube, and which isscrewed via an internal thread portion to said external thread portionof said joint body, a sealing portion being formed in an inner area ofsaid pipe receiving port by a tapered face which is smaller in diameteras one moves further toward an outer side in an axial direction and thenreaches an inner radial face of said joint body, said one end portion ofsaid tube into which said sleeve is pressingly inserted to be integratedtherewith being inserted into said pipe receiving port, said inner endsealing portion of said sleeve which is pressed against said joint bodyby fastening said union nut abutting against said sealing portion,thereby sealing a gap between said one end portion of said tube and saidpipe receiving port of said joint body, wherein a second shape of eachof threads of said external thread portion of said joint body and saidinternal thread portion of said union nut is formed as an asymmetricaltrapezoid, defining a first flank and a second flank and having anincluded angle of said first flanks of said asymmetrical trapezoidalthreads which contact with each other by fastening said union nut is setto 70 to 90°, and an included angle of said second flanks opposite tosaid first flanks is set to 40 to 80°, wherein said joint body defines asealing portion the angle and direction of taper of which is defined byan angle θ₀, said external thread is defined by an angle θ_(1,) andwherein θ₀<θ₁ and |cos θ₀|>|cos θ₁|.
 3. A pipe joint made of resin,comprising: a joint body which is made of resin, said joint body havinga pipe receiving port in one end portion, and an external thread portionon an outer periphery of said pipe receiving port; a sleeve which ismade of resin, which is to be pressingly inserted into an innerperiphery of an one end portion of a tube made of resin, and in which acylindrical sealing portion is formed in an inner end portion; and aunion nut which is made of resin, which has an internal thread portion,which is loosely fitted onto an outer periphery of said one end portionof said tube, and which is screwed via an internal thread portion tosaid external thread portion of said joint body an annular groove beingformed in an inner area of said pipe receiving port, said one endportion of said tube into which said sleeve is pressingly inserted to beintegrated therewith being inserted into said pipe receiving port, saidcylindrical sealing portion of said sleeve which is pressed against saidjoint body by fastening said union nut being pressingly inserted intosaid annular groove, thereby sealing a gap between said one end portionof said tube and said pipe receiving port of said joint body, wherein asection shape of each of threads of said external thread portion of saidjoint body and said internal thread portion of said union nut is formedas an asymmetrical trapezoid, defining a first flank and a second flankand having an included angle of said first flanks of said asymmetricaltrapezoidal threads which contact with each other by fastening saidunion nut is set to 70 to 90°, and an included angle of said secondflanks opposite to said first flanks is set to 40 to 80°, wherein saidjoint body defines a sealing portion the angle and direction of taper ofwhich is defined by an angle θ₀, said external thread is defined by anangle θ_(1,) and wherein θ₀<θ₁ and |cos θ₀|>|cos θ₁|.
 4. A pipe jointmade of resin according to claim 2, wherein sealing is performed betweenoverlapping faces of an outer periphery of said cylindrical sealingportion and an outer periphery in said annular groove.